I ended up turning off Spam Filtering and Antivirus, and the emails re-qued and delivered fine. So they I tried (using the admin console) turning each one on separately and trying it, and if either one are turned on they cause the emails to just cue up in the deferred list.

4.5.7 will include a different version of clamav that will probably solve your problem
-if you can't wait till the end of the week, you could try increasing the watchdog timeout or manually upgrading your clamav build